Python assign sign of number to variable

Question

I have a variable of type int, it's Python, so it can be positive and negative. Now, I want to make another variable have the same sign as the first variable1. It's easy to do this by using an if statement and then assign -1 or +1 to a variable and multiply every variable I want to have this sign by the -1 or +1. But then I thought maybe there is another way to do this (e.g. a built-in function). Is there something like "sign = getsignbit(value)"?

edit: Solved! math.copysign did the thing, cmp(x,0) works too, but I don't only want -1, 0 or 1, but also turn a 5 into -5.

sign = lambda x: math.copysign(1, x) looks good

yossi
– yossi

2013-11-01 20:57:23 +00:00
Commented Nov 1, 2013 at 20:57 — yossi
– yossi, Commented Nov 1, 2013 at 20:57

Community · Accepted Answer · 2017-05-23 11:51:54Z

There's no built in sign function (see this answer for some explanation: Why doesn't Python have a sign function? ), but math.copysign might be useful to you. http://docs.python.org/2/library/math.html#math.copysign

John · Accepted Answer · 2013-11-01 20:54:15Z

3

I don't think there is a built-in function, but you can roll your own easily enough:

def the_sign(num): return cmp(num, 0)

answered Nov 1, 2013 at 20:54

John

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2 Comments

Ashwini Chaudhary Over a year ago

Note that cmp has been removed in Python3.

user2746752 Over a year ago

I'm using Python 2.7, it works both but I like math.copysign better. I still gave a +1 though ;)

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